The present invention relates to the field of selective deposition of thin film metallization on a substrate for microelectronic interconnects. Laser assisted electroless plating has been discussed in the literature in which a laser beam is used to enhance the plating reactions by creating very localized heating. These methods suffer the drawback that the horizontal scan rate of the laser is constrained by the slow vertical electroless deposition rates. These slow vertical deposition rates are inherent in the physics of the process and are not likely to be increased substantially. This time delay may make direct laser write of plated metal impractical when hundreds or thousands of interconnections must be formed on a substrate.
Another technique for patterning metal on a substrate is by laser assisted chemical vapor deposition of a palladium catalyst, as disclosed in Baum U.S. Pat. No. 4,574,095. This method, however, uses a temperature controlled vacuum system during laser writing which requires a much more complex and expensive process than wet chemistry.
It is also well known that a polymer film which does not initially contain palladium can be patterned, and palladium can be subsequently applied to the patterned film to form a catalyst for electroless plating, as described in Hoover U.S. Pat. No. 4,666,735 and Jackson U.S. Pat. No. 4,701,351. In both of these methods, however, conventional photolithography techniques are used to pattern the polymer film; that is, a photoimagible polymer is exposed to light through a mask to create the desired pattern. In the case of the method in Jackson this photoimagible polymer is separate from the polymer which complexes the palladium.
Finally, in a paper by Cole, et. al. presented at the Electrochemical Society Meeting in October, 1987 a method is proposed in which palladium compounds are irradiated with a laser to selectively physically alter the palladium in such a way that only the irradiated areas are catalytic to electroless plating. One drawback of this method is that the film must cover the entire substrate prior to laser writing and therefore most of the palladium, an expensive material, may be wasted since in some applications only a small percentage of the substrate area will ultimately contain metal features.